1. Field of the Invention
The field of art to which this invention pertains is the solid bed adsorptive separation of a ketose from other ketoses and aldoses. More specifically, the invention relates to a process for separating psicose from a mixture comprising psicose, fructose and one or more additional ketoses, and/or aldoses which process employs an adsorbent comprising a calcium-exchanged Y-type zeolite to selectively adsorb psicose from the feed mixture.
2. Information Disclosure
The use of crystalline aluminosilicates in non-hydrocarbon separations is known, e.g., to separate specific monosaccharides or classes of monosaccharides from carbohydrate feed mixtures. A specific example of a class separation is given in U.S. Pat. No. 4,024,331 disclosing the separation of ketoses from a mixture of ketoses and aldoses using a type X zeolite. Specific monosaccharides such as glucose and fructose are isolated from a feed mixture containing the same by an adsorptive separation process using an X zeolite as taught in U.S. Pat. No. 4,442,285.
This invention is particularly concerned with the separation of a ketose, psicose, from another ketose, fructose, mixed with the aldoses, mannose and glucose. Heretofore, no feasible method for commercially separating psicose from the other products of isomerization of aldose sugars, e.g., glucose, was available. Therefore, enzymatic means rather than simple isomerization methods have been used for the production of fructose, because the enzymatic route minimizes the production of psicose. Now, with my discovery of a means for separating psicose from fructose, and other ketoses and aldoses, the simpler, less costly isomerization methods can be used to produce psicose-free fructose. There are two isomerization routes known for obtaining fructose from glucose, namely by the reaction of weak alkali on glucose and the reaction of hot pyridine on glucose. Chemistry of the Carbohydrates Pigman et al Academic Press Inc. NY, NY 1948, pages 41, 126-7. Similarly, isomerization of galactose by either of the isomerization techniques referred to above will produce a mixture of aldoses, talose and galactose and a mixture of ketoses, sorbose and tagatose and may be separated by means here disclosed. Furthermore, there is considerable interest in the various L-sugars, which are believed to be low in calories and possibly non-metabolized, which cannot be made enzymatically, but only by isomerization routes such as those mentioned above. This invention applies to the L-sugars as well as D-sugars, and is seen to be an advantageous method for obtaining L-fructose, free of contamination by L-psicose, as well as purified L-psicose.
Data related to potential adsorbents for the separation of mannose from other monosaccharides is set forth in U.S. Pat. No. 4,471,114. This patent contains data related to the use of a Y type faujasite exchanged with calcium cations as an adsorbent for the separation of mannose from glucose and other monosaccharides.
The separation of mannose from glucose is the subject of British Pat. No. 1,540,556. There the adsorbent is a cation exchange resin in salt form, preferably calcium form.
Neuzil et al U.S. Pat. No. 4,340,724 teaches the separation by adsorption of a ketose from an aldose with a Y zeolite exchanged with NH.sub.4, Na, K, Ca, Sr, Ba and combinations at the ion exchangeable sites or an X zeolite exchanged with Ba, Na or Sr and combinations thereof.
The separation of psicose from other ketoses is stated in U.S. Pat. No. 4,096,036 to be possible with ion exchange resins capable of complexing with a polyol at a first temperature and dissociating the complex at a second temperature in a thermal parametric pumping apparatus.